Critical low battery issue with Nook Tablet

Hi everybody,
I have purchased nook tablet recently and it works simply great.
But, from the last few days I am facing a strange issue. Even if It has more than 50% of battery life, it shuts down on its own saying critical low battery. It also starts flipping all the pages and it will pull all kinds of applications. If I connect to the AC adapter all the time, then only it will work.
Does anybody faced the same kind of problem ever? Please help me to resolve this issue. Thanks a lot in advance, guys!
